Combined steam cracker and butene dehydrogenation light ends



Oct. 27, 1964 R. P. cAHN ETAL 3,154,482

COMBINED STEAM CRACKER AND BUTENE DEHYDROGENATION LIGHT ENDS Filed Nov. 2, 195e Robert F? Cohn Robert H. Johnston Inventors By Edif H A.

` Potent Attorney products at atmospheric pressure.

3 1300 F. from line 17 and is passed through line 19, valve and line 21 to reactor 22 containing a fixed bed of a Reaction Conditions I General 'Specific Space Velocity ot 11 butenes, v. /v,/hr.\ 75-200 120 Space Velocity of Steam, v./v./nr.l 2, 300 Reactor Inlet Temperature, F 1, 175 Temp. Drop Across Reactor, F 70 Reactor Outlet Pressure, p.s.i,a. 20 n-Butylene Conversion, percent per pa 45 selectivity to Butadiene, percent 75-95 S5 1 V./v./hr.=volume of gas at S.T.P./volume catalyst/hour.

The euent from reactor 22 is passed through line 23 valve 24 and line 25 to cooler 26 where its temperature is reduced to 75-125" F., e.g., 100 F. About every minutes it is necessary to regenerate catalyst whereupon reactor 22 is swung from the stream by closing valves 20 and 24 and opening valve 27 which passes vapors through line 2S to reactor 29, containing a fresh bed of catalyst and the effluent gases are passed through line 30 and valve 31 to line 25 previously described. Regeneration of the catalyst in the off stream reactor is obtained at temperatures of 1000 to 1250 F., e.g., 1100 F. utilizing steam by conventional means not shown, space velocity of the steam in regeneration being 500 to 1500, e.g., 900 v./v./hour. Alternatively to the use of the above described catalyst and reaction conditions obviously other catalysts and reaction conditions can also be used. For example, the following described catalyst, reaction conditions, and regeneration can be utilized.

Chromia-alumina catalyst, 1000-1200" F., e.g., 1150 F. inlet temperature, 1-15 p.s.i.a., e.g., 3 p.s.i.a.; onstream time 7-15 minutes, eg., 10 minutes.

i For feed of 81% n butenes, 19% n butane. ohromia on alumina.

Since the reactors operate under vacuum, a compression step on the reactor etiluent, after quenching, is required, before it can be mixed with the steam cracker The two comingled streams are then further compressed to absorber pressure.

The effluent stream from cooler 26 is passed through line 32 to a separator 33 for removal of water from the bottom of said separator through line 34 if the calcuim nickel phosphate catalyst is used. The stream is thence passed through line 35 to join the steam cracker light ends eluent from separator 12 in line 13. Alternatively, if removal of water is not necessary the stream may be passed directly through line 32a to line 35.

The combined light ends from steam cracking and from butene dehydrogenation after compression in 3-stage compressor 14 are passed through line 36 to cooler 37 where their temperature is further reduced to about 75-125 Catalyst-2O wt. percent Cir F., e.g., F. The cooled stream is passed through line 38 to a further separator 39 wherein a predominantly C3 and lighter hydrocarbon gaseous stream is passed overhead through line 40 to an absorber for removal of H28. From the bottom of separator 3S? the heavier liquid materials are passed through line 41 to a naphtha splitter 42 wherein C@ and heavier hydrocarbon materials are taken otl as bottoms through line 43, the overhead material is passed through line 44 to a caustic scrubber 45 for removal of sulphur compounds and CO2 and the scrubbed liquid is passed through line 46 to absorber deenthanizer 47.

Returning to the predominantly C3 and lighter hydrocarbon material in line 40, this material is passed to absorber tower 48 vfor removal of HZS and CO2 where it is contacted with diethanolamine supplied through line 49. The absorbed material and solvent are passed through line 50 to diethanolamine regenerator 51, regenerated material being supplied through line 49 back to the absorber as previously described. From the top of the absorber, light ends are passed through line 52 to caustic wash tower 53, supplied with caustic through line 54, spent caustic being removed through line 55, and the stream is then passed through line 56 to absorber deethanizer 47. This tower is supplied with a C5 lean oil through line 57 and the C2 and lighter hydrocarbon material is passed overhead through line 5S to sponge oil tower 59 wherein traces of C5 lean oil are removed from the C2 and lighter hydrocarbon gas taken overhead through line 60. From the bottom of the absorber deethanizer i7 C3 and heavier hydrocarbon material is passed through line 61 to debutanizer tower 62, C5 material being removed from the bottom of said tower through line 63 and passed in part through line 57 as previously described and in part being passed from the system through line 64. From the top of the tower C4 and lighter hydrocarbon material is passed through line 65 to condenser 66 from which part of the stream is relluxed to the tower through line 67 and the remainder is passed through line 68 to depropanizer 69. Here the C3 cut is separated overhead through line 70 and the C4 cut is taken off as bottoms through line '71 to be passed to further processing including butadiene extraction not shown.

The present invention will additionally be understood from the following example illustrating the advantages of the present invention.

EXAMPLE Steam Cracking Feed, 7000 b./d., 350/700 F. gas oil kProducts contain 1380 mols/hour C3 and lighter hydrocarbons Out of which propene+propane=280 mols/hr. Also, we get C4s=157 mols/hr.

In an absorber-defenthanizer operating at 325 p.s.i.g. and 60 F. top temperature, lean oil requirements would be 805 mols/hr. The debutanizer, when operating with F. condensing temperature, will have to run at 170 p.s.1.g.

Butene Dehydrogenalon Feed 200 mols/hour C4, containing mols/hour n-butene. Catalyst, calcium nickel phosphate as above described.

At 45% conversion, the etiluent contains 82.5 mols/ hr. unconverted n-butenes.

The total reactor eliluent will contain:

104 mols/hr. C3 and lighter hydrocarbons (containing 6 mols/hr. propene). 220 mols/hr. C4s (butadiene, n-butenes, n-butane, ete).

Where this feed is supplied to an absorber-depropanizer, operating at 325 p.s.i.g. and 60 F., 25 mols/hr. of lean oil is required.

By combining the two absorbers, the lean oil rate is only 795 mols/ hr. or a saving of 805 mols/hr. -1- 25 mols/hr.

@l mols/ hr. 795 mols/ hr.

3.5 mols/ hr.

or over 4%. In all cases above mols are lb. mols.

Also, the debutanizer operating on the mixed feed case can operate at 132 p.s.i.g., when running with 110 F. condensing temperature.

Corresponding debutanizer bottoms temperatures:

Tower pressure, p.s.i.g.: Bottoms tem-p., F. 132 281 170 305 At 300 F., rapid fouling of reboilers, etc. is experienced. At 281 F. the rate of fouling .is much slower.

Although -a particular embodiment light ends system has been described the advantages described above will be obtained generally in all light ends systems. It is of course intended that Ithis invention cover the processing of a combined stream of butene dehydrogenation light ends .and steam cracking light ends in any of these systems.

It is to be understood that this invention is not limited to the specific example, which has been Ioffered merely as an illustration, and that modifications may be made without departing from the spirit of this invention.

What i-s claimed is:

1. An improved system for processing the light ends 4from a steam cracker and for processing the light ends from a butene 'dehydrogenation unit, which comprises combining the light ends Afrom a steam cracker operated to produce mainly -olens and diolens, said light ends comprising mainly C5 .and lighter hydrocarbons including C3 hydrocarbons, with fthe eluent from `a cyclic butene dehyd-rogenation unit, a fluctuation in the ow of product gases from .the butene dehydrogenation eluent being obtained during the replacement of the reactor containing spent catalyst with a reactor containing freshly regenerated catalyst, passing .the combined stream of vapors to a compressor wherein the pressure of lthe combined stream is raised to a high pressure of above about 150 p.s.i.g., and passing the high pressure stream to van absorption and fractionation light ends system for recovery of separate components from the stream.

2. The process of claim 1 in which the ratio of C4 to C3 components in the combined stream is in the range of 1.2 to 2/1.

3. The process of claim 1 in which the volume of the effluent yirofm the butene dehydrogenation unit is about 5-50% of the volume of the light ends from the steam cracker.

4. The process of claim 1 in which the high pressure combined stream is passed to an absorber deethanizer oper-ated using a C5 lean oil stream, and the C3 `and heavier hydrocarbons material `from `said absorber deethanizer is passed to a debutanizer operated at a pressure of below 140 p.s.i.g.

5. The process of `claim 1 in which the high pressure combined stream is passed to an absorber deethanizer operated using a C5 lean oil stream, the C3 and heavier hydrocarbons material from said absorber deethanizer is passed to a debutanizer operated at a pressure of below 140 p.s.i.g. and `a part of the C5 bottom stream from the debutanizer is used as the C5 lean oil in the absorber deethanizer.

6. The process of claim 1 in which butene dehydrogenation is carried out in the presence of steam and a calcium nickel phosphate catalyst and in which steam is condensed and removed from the etliuent stream Ffrom the butene dehydrogenation unit before combining said stream with the light ends from the steam cracker.

7. The process of claim 1 in which butene dehydrogenation is carried out in the presence of a chromia alumina catalyst.

8. An improved system for processing the light ends from a steam cracker and for processing the light ends from a butene dehydrogenation unit, which com-prises combining the light ends from a steam cracker operated to produce mainly olens and diolens, said light ends comprising mainly C5 and lighter hydrocarbons including C3 hydrocarbons, with the effluent lfrom a cyclic butene dehydrogenat-ion unit, said cyclic butene dehydrogenation being carried out in the presence of steam and a calcium nickel phosphate catalyst 'and a uctuat-ion in the flow of product gases from the unit being obtained during the replacement of the reactor containing spent catalyst with a reactor containing freshly regenerated catalyst, the volume of the eluent from the butene dehydrogenation unit being about 5-50% of the volume of the light ends trom the steam cracker, compressing the combined stream of vapors to a high pressure of above about p.s.i.g., passing the high pressure combined stream to an absorber deethanizer oper-ated using a C5 lean oil stream, passing C3| material from the bottom of said absorber deethanizer to .a debutanizer operated at 'a pressure of below 140 p.s.i.g. and passing a part of :the C5 bottom stream from the debutanizer back to the absorber deethanizer to be used as the C5 lean oil in said absorber deethanizer.

References Cited in the ile of this patent UNlTED STATES PATENTS 2,181,302 Keith et al. Nov. 28, 1939 2,382,473 Frey Aug. 14, 1945 2,391,555 De Simo et al Dec. 25, 1945 2,429,980 Allinson Nov. 4, 1947 2,458,082 Kilpatrick Jan. 4, 1949 2,745,889 Johnston et al. May l5, 1956 2,750,435 Fetchi-n June 12, 1956 2,831,041 Sieg et al Apr. 15, 1958 2,943,041 Johnston et al June 28, 1960 2,945,804 Henrm-inger July 19, 1960 2,972,646 Cahn et al. Feb. 21, 1961 

1. AN IMPROVED SYSTEM FOR PROCESSING THE LIGHT ENDS FROM A STEAM CRACKER AND FOR PROCESSING THE LIGHT ENDS FROM A BUTENE DEHYDROGENATION UNIT, WHICH COMPRISES COMBINING THE LIGHT ENDS FROM A STEAM CRACKER OPERATED TO PRODUCE MAINLY OLEFINS AND DIOLEFINS, SAID LIGHT ENDS COMPRISING MAINLY C6 AND LIGHTER HYDROCARBONS INCLUDING C3 HYDROCARBONS, WITH THE EFFLUENT FROM A CYCLIC BUTENE DEHYDROGENATION UNIT, A FLUCTUATION IN THE FLOW OF PRODUCT GASES FROM THE BUTENE DEHYDROGENATION EFFLUENT BEING OBTAINED DURING THE REPLACEMENT OF THE RE- 